Dinosaurs were creatures that ruled the Earth for over 160 million years. They became extinct in the Cretaceous period, 65 million years ago when an asteroid hit the earth causing the climate to change extremely leading up to the dinosaurs extinction. Many different species of dinosaurs existed during this time, about 500 different species in total.
Each species had different adaptations and different body parts to better their living conditions. Dinosaurs were reptiles and most dinosaurs hatched from eggs and grew relatively quick compared to the growth of humans. The largest dinosaurs were over 100 feet long and up to 50 feet tall. The smallest dinosaurs were about the size of a chicken.
Dinosaurs are grouped into different orders based on the structure of their hip bones. One order they can be grouped into is the order Ornithschian, meaning bird hipped. Even though these dinosaurs had hip bones similar to birds, they are not ancestors to birds. Dinosaurs that are grouped into the order Ornithschian are all herbivores, meaning they only eat plants or that they are vegetarians.
In some cases, they lived in herds which made it harder for the Saurischian dinosaurs to hunt them as the Saurischian dinosaurs usually lived in smaller groups. These dinosaurs had a pubis bone that pointed downward and towards the tail. This meant that Ornithschian dinosaurs had a four pronged pelvic structure.
They can also be grouped into the order Saurischian, meaning lizard hipped. In the order Saurischian, the majority of the dinosaurs are carnivores. Their hunting styles varied from group hunting and hunting alone. Usually if a saurischian dinosaur was relatively small, it would hunt in groups. Bigger carnivorous dinosaurs hunted alone and kept their own territory. Saurischian dinosaurs had three pronged hips and a pubis which rotated backwards. These dinosaurs were divided into two main groups; theropods and one of the two.